Typically, the handle or knob of a mortise lock has been connected to rotate a hub which carries opposite arms or cams which move against a retraction lever for retracting the latch bolt. In early cases, the opposite arms or cams engaged the retraction lever at widely separated points so that the lever arms were quite different for different directions of knob rotation, and in consequence, the torque required was much greater for one direction of rotation than for the other. An example of this is shown by the McCarter U.S. Pat. No. 2,086,982 of July 13, 1937. One proposal for reducing this torque difference has been to utilize a so-called scissors lever arrangement in which rotation of the knob hub in one direction acts directly on the retraction lever while rotation in the opposite direction acts on a secondary lever pivotally interconnected to the retraction lever. This does not completely eliminate the torque difference, and is relatively complicated and expensive. Examples of this are shown in Foster U.S. Pat. No. 3,361,462 of Jan. 2, 1968, and in FIGS. 2-5 of my U.S. Pat. No. 4,389,061 of June 21, 1983. Still another proposal has been to interpose a slide between the hub and retraction levers so that rotation of the knob hub in either direction produces linear movement of the slide which is transmitted to the lever at substantially the same point for both directions of knob rotation. This interposes additional mechanism and additional cost. An example of this is shown in the Alexander U.S. Pat. No. 4,118,056 of Oct. 3, 1978.
The present invention provides for the retraction of the latch bolt of a mortise lock by the application of a relatively low torque on the knob or handle, which torque is substantially the same for both directions of rotation of the knob or handle.